This research is focused on the investigation of selected urban and soil surfaces for their potential to serve as sources and/or sinks of nitrous acid to/from the atmosphere. Nitrous acid is an especially important compound in atmospheric chemistry because of its ability to serve as a precursor to the formation of the hydroxyl radical and thereby influence the oxidizing capacity of the atmosphere. Current chemical models are unable to reproduce the observed profiles of atmospheric nitrous acid, due in part to the fact that its sources and sinks are not well understood. Recent studies suggest that significant daytime production of nitrous acid may be attributed to heterogeneous reactions on various environmental surfaces, such as asphalt, cement, and soils.
Laboratory studies will be conducted to generate the kinetics and photochemical data needed to advance predictive models of ambient nitrous acid (HONO) levels. This research will determine the reaction probabilities for (a) the uptake of HONO on soil, asphalt, and cement; and (b) nitrogen dioxide (NO2) conversion to HONO on iron oxides and asphalt under atmospheric conditions. Measured uptake coefficients will help to constrain the fraction of HONO that may be loss to boundary layer surfaces. The quantum yields of HONO formation and molar absorptivity values measured for nitrate adsorbed to surfaces (such as soil) are key parameters that will enable calculations of HONO fluxes from these sources.